1. Field of the Invention
The present invention relates to a connection admission control system and more particularly, to a connection admission control system based upon fuzzy control.
2. Description of the Related Art
A broadband ISDN (Integrated Service Digital Network) has been researched and developed as a next generation communications network by which all the communications services (voice, data, moving image, etc.) can be integrated. ATM (Asynchronous Transfer Mode) is a technique for converting all the information into fixed information (referred to as cells) for enabling higher information transfer, irrespective of the continuous information such as moving image, the occurrence of burst information such as data, and the respective communication speed thereof.
However, since the ATM processes the various traffics of different information speeds and different burst conditions (the status in which a great amount of information occurs momentarily) in the respective services, in particular when the traffics of high burst conditions are mixed with each other, there exists a problem in that it is impossible to provide a service quality (e.g., with respect to the cell disuse ratio, delay, etc.) required by the user. Accordingly, it has become necessary to provide any control system for accepting or rejecting an incoming call, in order to secure the high service quality required by the users.
FIG. 4 is a schematic block diagram showing a prior art variable speed communication system. In the drawing, the system is composed of a plurality of B-ISDN terminals (B-TE), an ATM switching system 2 constructed by ATM switches 2a, and a central control unit (CC) 10 connected to the ATM switch system 2 to control the switching operation of the ATM switches 2a. Further, traffic parameters are stated (reported) to the central control unit 10 by the B-ISDN (wide bond) terminals 1 (referred to as users or subscribers).
In the system as described above, the control procedure to a call is as follows: when the user first states the traffic parameters such as a maximum speed, an average speed, etc. of the communication service now requested, on the side of the ATM switching system 2 the central control unit 10 calculates an estimated band which satisfies the user's communication service quality (the cell disuse ratio, the cell transfer delay, etc.) on the basis of the stated parameters and in accordance with complicated calculations. Further, if the estimated band can be accommodated in a currently idle band of the transmission line, the system accepts the call. However, if not accommodated, the call is rejected.
FIGS. 5(a) and (b) are illustrations for assistance in explaining the call allocating method, in which FIG. 5(a) is an example of fixed allocation and FIG. 5(b) is an example of variable allocation. In these figures, transmission line speeds (bandwidth) are allocated within the width of the XMSN transmission line 3. In the case of the fixed allocation method as shown in FIG. 5(a), four channels of A to D are allocated, for instance. In this system, since the bandwidth are fixedly allocated, there exists a problem in that the degree of freedom of the band availability is small and therefore it is impossible to use the transmission line effectively.
In contrast with this, in the case of the variable allocation method as shown in FIG. 5(b), since the used band varies for each channel as shown, the statistical multiplex communications are enabled in such a way that the crest of a channel overlaps with a trough of the other channel, so that it is possible to allocate an additional channel E to the same transmission line, thus improving the availability of the transmission line.
However, where the statement of the traffic parameters and the estimation of the band are executed strictly, there exists another problem in that a huge calculation time is inevitably required. FIG. 6 is a graphical representation showing the traffic characteristics of the system, in which the number of calls of the same sorts is taken on the abscissa and the band is taken on the ordinate. In the drawing, P denotes the stated peak band value, and Vm denotes the stated averaged band value. In practice, however, the band characteristics become as shown by the curve f in FIG.6. In other words, there exists a non-linear range in which the peak value p changes to the average value VM between the area (where the number of calls n is small) and the area (where the number of calls is large). Therefore, when this non-linear range is required to obtain as the estimated band, various complicated calculations are necessary as already described.
As the method of calculating the estimation band, a statistical method based upon a binomial distribution approximation is known as disclosed by "Call Acceptance Control System in ATM Switching Network" 1990 Preliminary Manuscript Collection of Great Spring Meeting of Electronic Information Communications Society, 3-421 pages SB-7-6, for instance.
In addition, techniques of adopting the fuzzy theory to a communication network are disclosed by 1991 Preliminary Manuscript Collection of Autumn Meeting of Electronic Information Communications Society and Electronic Information Communications Society Transactions B-1 Vol. J72-B-I No.7 pp 555-563 (July, 1989), for instance.
However, after the traffic parameters have been stated, when the band is estimated strictly in accordance with these methods, a huge calculating time is required and thereby constitutes a hindrance to the switching processing.
To overcome this problem, it is possible to estimate the band in accordance with a more simple method of calculating the band estimation value by use of traffic parameters simple to some extent. In the simple method of calculating the band estimation, however, since the band is not estimated strictly and therefore set to the more safer numerical value for securing the service quality, there raises another problem In that the estimated band occupies the band more than necessary, thus decreasing the efficiency in availability of the transmission line.
On the other hand, although there exists an attempt to execute the connection admission control in accordance with the fuzzy theory, as described above, it has been so far not clear as to practical means for controlling the connection admission and the practical system configuration thereof.